Extruding faces along normals to do a roll
You can easily CtrlLMB  to extrude towards the mouse. (if you are talking about making the curved back)





If you are just trying to make the edge rounded (a Subsurf modifier will help will the smooth roundness) add an edge loop on the out side edge. The pink line in the image below is the new edge loop.


Then switch the Transform Orientation to Normal and move the new edge along the normal Z.